Consolidation (weeks 10-19): Patients must have M1 marrow to proceed. Patients receive oral mercaptopurine on days 70-126; methotrexate IV over 24 hours on days 77, 84, 91, and 98; leucovorin calcium IV or orally every 6 hours on days 78-79, 85-86, 92-93, and 99-100; and methotrexate IT on days 77, 84, 91, and 98.